The production of helical teeth in gear wheels by means of a hob is known for a long time. It is mostly done by axial generating methods. It is also known to produce helical teeth by means of the diagonal generating method, i.e. the feed occurs both axially and tangentially. The tooth flanks are not formed accurately but approximated facet-like by a finite number of generating cuts. Every generating cut of the generating cut profile is tangent to the theoretical involute profile in one point while all other points deviate to a greater or lesser extent from the involute profile. The scalelike surface structure is smoothed out by a subsequent finishing process such as generative grinding. The theoretical exact involute profile is altered for optimizing bearing behaviour and minimizing noise development. It is common practice to generate a specific profile crowning (tip relief) to achieve a hitchless operation. Profile crowning or tip relief is accomplished by appropriately profiling the tool's flanks. A correction of the flank geometry over the width of the tooth space, i.e. a specific helix crowning or conicity of the tooth space and slope of the crowning is achieved either through movements of the workpiece or movements of the tool that vary the axial space between the tool and the toothed gear passing the tooth space in axial direction. With spur geared cylindrical gears this method leads to the desired result. In case the shaft angle between workpiece and tool differs from 90°, the contact ratios cause an unequal correction of the corresponding left or right flanks of a tooth space.
It is known from “Pfauter-Walzfräsen” Teil I, Verfahren, Maschinen, Werkzeuge, Anwendungstechnik, Wechselräder, Springerverlag p. 436, the entire contents of which is incorporated herein by reference, to use hobs with different tooth thickness and tooth profile in axial direction for the production of helix crowned gearing and to work with the diagonal generating method. In this process the hob is set, so that its widest tooth space comes in operation at the center of the workpiece gearing thus forming the biggest tooth thickness there. Thicker cutting teeth work at both ends, i.e. the workpiece teeth get thinner there (double-duplex-character).
DE 37 04 607 A1, the entire contents of which is incorporated herein by reference, discloses a method, that allows longitudinal corrections of the gear teeth by varying distances and avoids their disadvantageous distortions at the same time. With the known method a worm grinding wheel is used in continuous diagonal generating method, whereas the pressure angle of the right and left flanks decreases continuously starting from a maximum value from one end of the worm to the other end. Coming at this from the knowledge that in every area a tooth space—in axial direction of the toothed gear—is related to a certain axial area of the worm. Since the geometry of the flanks of the worm's windings varies in axial direction, the tooth space to be created is generated over the width of the tooth space by a permanently changing tool. During the grinding movement between workpiece and tool the worm is not only scrolled axially to the workpiece but also tangentially, so that the approach area of a tooth space is processed by different worm windings than the recess area of that tooth space, viewed over the height and width of the workpiece respectively. In order to achieve the desired corrections on the involute teeth on the one hand and to avoid the described distortions on the other hand, the flanks of the worm gear of the worm tool have different pressure angles, i.e. pressure angle and tooth thickness vary from one end of the tool to the other end, so that their distortion effect is compensated in connection with an axial correction.
The known method requires that first of all the workpiece is pre-profiled by means of a roughing hob, usually after the axial generating method. Afterwards, it has to be finished for instance with a gear grinding machine in order to achieve a correction by means of the described worm grinding wheel. Naturally, this is associated with increased production complexity.
Before or after the finishing the teeth of a toothed gear have to be deburred or bevelled, respectively. For this purpose several methods became known.
Additionally, from DE 203 20 294, it became known to mount a deburring cutter on the same tool shaft as the finishing hob. The deburring cutter resembles a disc milling cutter, its cutting teeth being helix curved and the deburring cutter being formed multithreaded with at least one tooth per gear. In this manner both the hobbing and the deburring occur in the continuous cycle. The tool shaft of hobbing machines is adjustable in space as is generally known. Finishing the hobbing process the hob is adjusted so that the deburring tool can be engaged with the leading edges of the tooth profile by rotating with the shaft in order to process the leading edges of the tooth profile consecutively according to the hobbing process.
The object of the invention is to provide a tool arrangement that can be used to produce a deburred and bevelled helical gearing for spur gears with little complexity in such a manner, that the gearing is twist-free